First off, please try and change the schedule so that the kitten does not leave its mother until 8 weeks old. This is the minimum recommended age to re-home a kitten. If its going to be an only cat (which I'm assuming, since you don't seem so keen to have one, let alone two) there can be psychological problems in the future if you remove from mother at only six weeks.
Because of this, I would be concerned that your girlfriend has not thought this through and may only want a cute kitten. They grow up. They are armed with sharp weapons. You don't want a disturbed adult kitty with that weaponry.
You need to decide if it is going to be an indoor or outdoor cat. This decision will influence a lot of further decisions, particularly on things like litter trays and house training/keeping it amused.
You will need to plan for the four to six month point when it will be neutered. Under no circumstances allow a cat to remain 'whole'. There's way too many unwanted kittens in the world. This can be expensive (not enormously, but depends on your means). Also, for male cats particularly, not getting it done early can mean spraying. And believe me, you don't want to be in a house that has a spraying cat.
If you intend to have an indoor cat, best to feed it dry food. This radically reduces any smell from poo, and there are many different types that can moderate things such as fur ball tendencies, getting overweight, issues from sterilisation etc. Choose a good litter and ideally a covered litter tray (cats don't like being watched when going to the toilet, and well behaved cats like to bury their doings well, which can lead to litter being showered over the floor - a cover reduces/prevents this without discouraging the cat from burying things - which is good behaviour you want to encourage).
If it's an outdoor cat, be prepared for dead things. Or semi-alive things. My cat has brought home everything from a decomposing shrew collection running to twenty plus corpses to a still furious fully grown seagull that covered the house in unimaginable shite. Oh, and next door's pet rabbits. Also, if you live near busy roads, be prepared for the unutterable heartbreak of your beloved pet being killed. Cats are enormously intelligent but they don't get the concept of cars. (I once had a wonderfully clever siamese who crossed the road using the pelican crossing. He was very social and would wait with the people and cross with them. He was killed one early morning on the crossing, where he had no-one to press the button so had marched across safe in the knowledge that this was where it was correct to avoid the cars. He was hit by a speeding car).
Happy to try and help whenever something comes up - but please, please don't get the kitten until it's eight weeks at least.
